Internal combustion engines generally use the torque supplied by the internal combustion engine at the crankshaft to control and regulate the internal combustion engine. The reference variable in this control is a setpoint torque. This setpoint torque can be input by the driver via a particular position of the accelerator pedal or by various systems of the motor vehicle such as an electronic stability program, traction control system or the control of an automatic transmission, for example. The control and regulation of the internal combustion engine translates the setpoint torque into corresponding control actions of, for instance, the throttle valve, the ignition timing, fuel-injection blank-outs, etc.
The torque supplied by the internal combustion engine is not measured directly in these internal combustion engines, but calculated via, for instance, a mass air-flow sensor as well as the lambda probe and corresponding models of the internal combustion engine. However, this calculation is sufficiently precise only in the case of Otto engines having manifold injection. In Otto engines having direct gasoline injection or in diesel engines, there is no clear correlation between the air mass aspirated by the internal combustion engine and the torque output by the internal combustion engine.
Compared to an internal combustion engine having manifold injection, in stratified-charge operation (lambda>1) and homogenous lean-mixture operation there are the following changed margin conditions in internal combustion engines having direct gasoline injection (DGI):
The air mass is no measure for the torque supplied by the internal combustion engine since only the injected fuel quantity is determinative of the torque.
A measurement of the exhaust gas composition with the aid of a continuous lambda probe is too imprecise.
The torque-affecting actuating variables are more numerous in internal combustion engines having direct injection. In particular, the start of injection, the exhaust-gas recirculation rate, the lambda value and the position of a throttle valve must be taken into account.
The calculation of torque Meff output by the internal combustion engine on the basis of the aforementioned measured influence variables can therefore be realized only by setting up numerous models and a complicated application of these functions in a control device. Nevertheless, the accuracy of such a determination of the torque supplied by the internal combustion engine is unsatisfactory, so that, for instance, drivability problems of the motor vehicle may arise in interaction with an automatic transmission. In addition, the inaccuracies in determining the torque supplied by the internal combustion engine may lead to increased fuel consumption since large safety margins must be observed in the application of operating limits for different operating types. Monitoring of the internal combustion engine with a view toward an unintentionally high torque output by the internal combustion engine is barely able to be implemented.
German Published Patent Application No. 197 49 434 describes a method for controlling an internal combustion engine in which the torque output by the internal combustion engine is determined with the aid of a pressure sensor, which records the pressure in the combustion chamber of a cylinder, and an angle-of-rotation sensor, which records the position of the crankshaft. In order to individually record the torque for each cylinder of the internal combustion engine, a separate pressure sensor is required for each cylinder. Because of the pressure sensors required for each cylinder, the implementation of this method entails considerable expense.